Optical scanning device

ABSTRACT

An optical scanning system embodying a rotatable drum having a series of mirrors arranged along its inner surface, a focusing lens system for directing an image onto an angled mirror located within the drum and on the axis of the system, the angled mirror directing the image onto the series of mirrors on the drum, the mirrors in the series being tilted at successively greater angles whereby as the drum rotates each mirror will effectively perform a line scan of said image directing the radiation from successive points along said scan toward a rotating mirror mounted on a galvanometer adjacent the axis of the rotating drum, the rotating mirror directing said scan to a remote detector.

73,532,8 1 w --e 7 7 s, v 'Et. q I

.vflnw. 3,632,871

[72] Inventors Robert A. l78/7.6 Santa Barbara, CBIIL; FOREGN PATENTSRichard F. Schuma, Lynnfield, Mass.

[ pp No. 819,283 21,696 9/1930 Australla 178/7.6

[22] Filed Apr. 25, 1969 Primary Examiner-Robert L. Griffin [45]Patented Jan. 4, 1972 Assistant Examiner-Joseph A. Orsino, Jr.

[73] Assignee Raytheon Company Attorneys-Harold A. Murphy, Herbert W.Arnold and Joseph Lexington, Mass. D. Pannone [54] OPTICAL SCANNINGDEVICE ABSTRACT: An optical scanning system embodying arotatal8Claims,8Drawing Figs. ble drum having a series of mirrorsarranged along its inner 52 us. Cl l78/7.6, a musing lens system dimmingimage angled mirror located within the drum and on the axis of thesystem, the angled mirror directing the image onto the series {2 g gg gof mirrors on the drum, the mirrors in the series being tilted at 50/6successively greater angles whereby as the drum rotates each mirror willeffectively perform a line scan of said image directl78/DIG. 27, 350/7,350/285 [56] References Cited ing the radiation from successive pointsalong said scan toward a rotating mirror mounted on a galvanometeradjacent UNITED STATES PATENTS the axis of the rotating drum, therotating mirror directing said 3,345,460 10/1967 Betts l78/7.6 Scan to aremote detector.

DUAL BEAM PHOTO mgggt' f os |LL0 coPE J CELL GENERATOR L 80 75 zoeruzcnou WAVEFORM 2:231 GENERATOR 36-3287; NOORCQASSIF.

msmmm 4m: (632,871

SHEET 2 BF 5 INVENTORS ROBERT A. WATKINS 'R/CHARD F. SCHUMA BY WM-ATTORNEY PATENH-In JAN 4m: 3,632,871

ROBERT A. WATKINS RICHARD F. SCHUMA BY'%MWM ATTORNEY BACKGROUND OF THEINVENTION This invention relates to optical scanning systems and moreparticularly to a drum scanner adapted to produce a raster scan.

Optical scanners are used to synthesize a picture of an object byobserving sequentially various portions of the object. The radiationfrom these various portions is processed and used to drive displayelements properly positioned to provide the complete picture. Typically,each portion is in the form of a strip extending across the picture. Thestrip can be scanned by a light-sensitive detector with an optical aid,such as a moving mirror, which permits the detector to be stationary.The detector senses the intensity of the light as the strip is scannedto provide a record known as a line scan. Each strip or line is scannedsequentially in a format known as a raster scan. The quality of thesynthesized picture depends on the purity of the signal received by thedetector, the linearity of the scan, as well as on the number ofscanning lines in the raster.

The development of a raster scan with a display device having fewerelements than the number of horizontal lines reproduced requires bothhorizontal and vertical scanning. Accordingly, the typical scanningsystem develops a plurality of horizontal scans and shifts the scanningbeam vertically between each of the horizontal scans. A typicalwell-known scanning drum carries mirrors which sequentially intercept animage-forming beam and provides only horizontal scanning so that anauxiliary scanning device is required to produce the vertical shiftsbetween the horizontal line scans. It is desirable, therefore, toprovide a scanning device which produces both the horizontal andvertical components of a raster scan by means of a single-mechanicalmotion in one direction.

Also, a major factor influencing the purity of the signal at the outputof the scanning device is the detector-receiving optics. For example, ifthe detector has a field of view wider than that subtended by theimaging optics, the detector senses the background radiation in additionto the signal beam of light. On the other hand, a scanning system whichprovides a matched field of view to the detector as limited by theimaging optics enhances the signal purity by eliminating a large portionof the photon noise generated by the background radiation. Furthermore,the matched field of view permits the use of a large relative aperturefor the detector which increases the intensity of the optical signalpresented to the detector and thereby provides a corresponding reductionin the effect of any noise produced within the detector itself.

However, a wide field of view is usually required for detectors usedwith such scanning devices. These scanning devices typically provide anoptical system wherein the image transmitted to the detector is notstationary, as for example where the image is reflected from a mirroraffixed to a rotatable drum wherein the point of reflection changes asthe drum rotates. Accordingly, the detector must have a sufficientlywide field of view to receive the optical signal in which the point ofreflection moves about its mean position. Therefore, the desirablenarrow field of view is not available for detectors in the typicaloptical scanner.

The aforementioned movement of the point of reflection in a simple drumscanner also introduces a defocusing effect.

The defocusing generally results from the radial motion of the drummirrors, with respect to the scanned planar image. Furthermore, with thetypical scanner of the prior art, less than half of the time is used incollecting scene radiation. This reduces signal purity. In certainsituations, such as where a moving object is to be scanned, rapidscanning can be obta ned by compromising picture quality for scanningspeed,

that is, the raster scans are produced at a higher rate, which 70further reduces signal purity or fewer line scans are produced perraster resulting in a coarse rather than a fine-line picture. It wouldbe desirable, therefore, to increase the number of line scans for agiven rate of drum rotation and to make full use of An object of thepresent invention is to provide an improved drum scanning device inwhich a single rotation of the drum produces both the horizontal andvertical components of a raster scan, and thereby eliminates the needfor an auxiliary g device to produce the vertical shifts between thehorizontal t line scans.

A further object of the present invention is to provide an opticalscanning device in which the detector is provided with an optical systemhaving a field of view which is better matched to the cone of radiationfrom the image-forming optics to enhance the signal purity.

SUMMARY OF THE INVENTION An optical scanning system comprising arotatable drum having a series of independent reflecting means locatedaround its circumference, focusing means such as a lens system fordirecting image-forming rays of radiation onto said reflecting meansfrom a stationary point substantially equidistant from each of saidreflecting means, each of said reflecting means being tilted atsuccessively different angles with respect to mind drum whereby as thedrum rotates each of said reflecting means performs a separate linescan, a rotatable means including radiation detecting means 2 positionedto receive image-forming rays of radiation which BRIEF DESCRIPTION OFTHE DRAWINGS The aforementioned objects and other features of theinvention are explained in the following description taken in connectionwith the accompanying drawings wherein:

FIG. 1 is an isometric view partly in block diagram form of the opticalsystem ofthis invention;

FIG. 2 is a sectional view of a scanning drum of the optical systemtaken along the axis of the scanning drum of FIG. 1;

FIG. 3 is a sectional view of a scanning drum of an alternativeembodiment of the invention in which prisms are utilized in the opticalscanning drum;

FIG. 4 is a sectional view of a scanning drum of an alternativeembodiment of the invention in which a radiation detector is rotatablymounted approximately in the center of the scanning drum;

FIG. 5 is an isometric view of an alternative embodiment of theinvention in which a multiplicity of radiation detectors are utilized inconjunction with sampling circuitry to provide a visible display of thescanned image;

FIG. 6 shows waveforms of the vertical deflection signal utilized in anoscilloscope display of the embodiment shown in FIG. 5;

FIG. 7 is an isometric view partly in block diagram form of an alternateembodiment of the invention in which the primary focusing lens combinesprismatic elements which are rotatably mounted to provide the verticalportion of the 5 scanning raster; and

FIG. 8 is a detailed view of the rotatable prismatic focusing lens,including a drive mechanism in diagrammatic form.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2 there is shownan embodiment of the present invention in which a rotating scanning drum 20 having ig settle of mirrorsglwhich armmfi'inner surface and wllirretiljtgd in a noilel-manneriv'ith respect to the drum axis performssequential line scans corresponding to the the available time in anyline scan to improve the signal purity. lines of a raster scan bydissecting an image of a scene, in particular object 24, to be scanned.The image of object 24 is formed from radiation emitted by object 24,such as visible or infrared radiation indicated diagrammatically byarrows 26, which passes through an image-forming converging lens 28 andis then incident upon a stationary inclined mirror 30 located at thecenter of the scanning drum 20. The inclined mirror 30 reflects theimage-forming rays of radiation radially outward so that these rays areintercepted by the rotating drum mirrors 22. Each of the drum mirrors 22successively passes through the image-forming rays of radiation anddissects the image by directing the radiation from a particular point inthe scene back to galvanometer mirror 32 and ultimately to radiationdetector elements 33. Thereby the image is dissected into a well-knownraster scan format having typically a set of horizontal line scans whichare vertically spaced from each other in accordance with the angles oftilt of the individual drum mirrors 22. The number of horizontal linescans generated with each detector element in this embodiment of theinvention is equal to the number of drum mirrors. Thus, the scanningdrum with its tilted mirrors provides both horizontal and vertical scanwith a single-mechanical motion.

To extract the scanned image, a rotatable galvanometer mirror 32 ismounted within a central aperture 34 of the inclined mirror 30 and onthe axis of the scanning drum 20 to receive sequentially from each ofthe tilted QEU ITJnlIILQIS 22; the reflections of the scanned imagewhich come to a focus? the galvanometer mirror 32. Lens 28 provides aspherical image surface having a radius, or back focus, approximatelyequal to the diameter of drum 20 thereby allowing the rotating drummirrors to remain equally spaced from the image surface, so that thegalvanometer mirror 32 remains on the focal surface as reflected by thevarious drum mirrors 22, so that each portion of the scanned image isclearly formed on the galvanometer mirror 32. Accordingly, the lens 28is placed a shirt distance, on the order of one diameter of lens 28, infront of inclined mirror 30 to provide the desired relationship betweenthe back focus of lens 28 and the radius of drum 20. The galvanometermirror 32 rotates in a cyclical fashion which is synchronized in amanner to be described with the rotation of each of the drum mirrors 22such that the galvanometer mirror 32 rotates in the same direction asthe scanning drum 20 and at one-half its rotation rate during the periodof scanning by a particular drum mirror, such as the drum mirror 22A. Atthe conclusion of this period, the galvanometer mirror 32 rotatesrapidly in the reverse direction to bring itself into position toreflect light from the next drum mirror 22. Thereby the rotation of thegalvanometer mirror 32 compensates for the motion of the cone ofradiation incident upon the galvanometer mirror 32 so that the imageswhich focus on the galvanometer mirror 32 are reflected in a cone ofradiation having a substantially fixed direction to a stationary relaysystem such as mirror 36, lens 44, and detector 33 for subsequentdetection and display. The relay mirror 36 is conveniently mountedwithin the scanning drum 20 to one side of the cone of radiation fromdrum mirror 22, and, accordingly, the galvanometer 40 is positioned atan angle so that radiation from each of the dmm mirrors 22 is reflectedto the relay mirror 36, The galvanometer mirror 32 has a lengthindicated by L and width indicated by W in FIG. 1 adequate to containthe images of the elements of the object 24 that are instantaneouslybeing viewed. The size of these instantaneous image elements is set bythe size of a detector element 33 as imaged by relay lens 44 on thegalvanometer mirror 32. The optical characteristics of relay lens 44establishes the cone within which radiation must pass in order to reachdetectors 33. Galvanometer mirror 32 redirects the diverging cone fromthe appropriate scanning mirror 22 to this lens 44. The cones ofradiation from the adjacent scanning mirrors are reflected fromgalvanometer mirror 32 in directions away from relay mirror 36 and lens44. Thus only a single-drum mirror 22 is in a position to directradiation to the detector at any one time. A plurality of radiationdetectors 33, two of which are designated 33A and 33B, are verticallydisplaced from each other with reference to the horizontal line scansand are located at a place of convenience away from the scanning drum 20to subdivide each scanned portion into a set of fineline scans. Totransfer the line scans to these detectors 33, the cone of radiationincident upon relay mirror 36 is reflected by the relay mirror 36 torelay focusing lens 44. Lens 44 focuses the radiation to form a secondimage of object 24 upon radiation detectors 33A and 33B. Due to thesubstantially fixed direction of the radiation incident upon the relaylens 44, the design of the relay lens 44 and mirror 36 is simplified inthat the cone within which the radiation lies at various times duringthe scanning process is essentially a cone from a fixed, nearly axialpoint. Thus, the relative aperture of the optical system comprising therelay lens 44 and mirror 36 can be increased beyond that of a lens andmirror system utilized for a nonstationary cone of radiation, therebyincreasing the intensity of the second image and providing a simplifiedoptical design for a given quality of the second image. That is, thebeams of radiation reaching detectors 33 are also substantiallystationary which permits the use of the radiation detector 33 sensitiveto the desired radiation and having a narrower receiving angle than forexample, that of another detector utilized for a nonstationary beam ofradiation, thereby improving the detectivity of the radiation by virtueof a reduction in the background photon noise.

The scanning drum 20 is rotatably supported within a rigid metallichousing having three rollers 52 which are covered with a shock-absorbingmaterial for reducing vibrations, such as rubber, not shown, and whichare disposed in equally spaced relationship around the periphery of thescanning drum 20 to support the drum 20 during rotation. The scanningdrum 20 has a slight circumferential depression, not shown, along itsouter surface to accommodate the rollers 52 and thereby guide the drum20. Rotation is imparted to the drum 24) through a belt 54 in frictionalcontact with the drum 20 and with motor pulley 56 on drive motor 58.

The rotation of the galvanometer mirror 32 is synchronized to therotation of the scanning drum 20 by means of a plurality of reflectors60, each of which is mounted on the outer surface of the scanning drum20 respectively with a preset circumferential distance from itscorresponding drum mirror 22 so that the rotation of the drum 20progressively positions each of the reflectors 60 to momentarily reflecta beam of light 62 from lamp 64 to scan line photocell 66. Photocell 66is responsive to the succession of light pulses from the reflectors 60and generates a corresponding succession. of output electrical pulseswhich trigger sawtooth current generator 68 to generate an electricalcurrent having a generally sawtooth waveform which is transmitted alongconductors, indicated diagrammatically by line 70 to the drive coil, notshown, of galvanometer 40 and causes the mirror 32 to rotate in theaforementioned cyclical fashion. The sawtooth waveform is composed of asuccession of ramp waveforms, each of which is synchronized to acorresponding triggering pulse from the photocell 66, and, therefore,the rotations of the galvanometer mirror 32 occur in synchronism withthe succession of light pulses from the reflectors 60. The sawtoothcurrent generator 68 is also equipped with a variable delay adjustment,not shown, utilizing well-known electrical circuitry to initiate eachramp waveform at the appropriate time relative to the triggering pulsesfrom photocell 66, and a current amplitude control, not shown, to adjustin a well-known manner the sawtooth current amplitude to provide therequired angular rotation of the galvanometer mirror 32.

The galvanometer 40 is of a well-known tubular form which typicallycomprises a rotatable coil of conductive material, not shown, mounted ona torsion support 41, directly connected to the mirror 32, and astationary magnet 42, positioned with its pole pieces in registrationwith the ends of the coil when the coil is in a neutral position ofrotation. The coil generates a magnetic field in response to thesawtooth current of sawtooth generator 68, shown in FIG. 1. The coil andthe mirror 32 are rotationally positioned by the action of the magneticfields of the coil and the permanent magnet which tends to rotate thecoil and mirror against the restraining force of the torsion suspension.The coil and mirror are held in a position of equilibrium for which themagnetic torque is equal and 0p posite to the spring torque.Accordingly, in response to the excitation of the drive coil by thesawtooth current generator 68, the coil and mirror 32 undergo anoscillatory rotation in which the angle of rotation or mirror 32 variessubstantially in the manner of a sawtooth waveform composed of asuccession of ramp waveforms with a rapid retrace from the end of eachramp to the start of the next ramp. For example, a high frequencyresponse of 2 kilohertz is desirable for a 100 hertz sawtooth waveform.The rotational inertia of the coil, torsion suspension and mirror issufficiently small to permit a fast retrace with high scanningefficiency which is frequently defined as the ratio of the time duringwhich useful scanning is accomplished to the total time.

The image of object 24 which has been dissected by the scanning drum 20,galvanometer mirror 32, and detector 33 is reconstituted into a visibleimage by a raster scan which is conveniently displayed in the case oftwo detectors 33 on a well-known dual beam oscilloscope 72 having a dualbeam cathode-ray tube, not shown. The electrical signals generated bydetectors 33A and 33B in response to the intensity of the detectedradiation are transmitted by means of conductors indicateddiagrammatically by lines 74 and are displayed on oscilloscope 72 byapplying each signal respectively to the beam modulation electrode ofeach beam of the cathode-ray tube. A well-known horizontal deflectionsignal having a generally sawtooth waveform for sweeping each electronbeam of the cathode-ray tube simultaneously across the face ofoscilloscope 72 is generated by a well-known deflection waveformgenerator 76 and is synchronized to the rotation of the drum 20 by meansof the electrical trigger pulses from scan line photocell 66 to providea horizontal sweep which is adjusted to the period of scanning by eachdrum mirror 22. Deflection waveform generator 76 also generates once foreach frame of the raster scan two well-known vertical deflection signalsfor controlling respectively the vertical deflections of each of the twoelectron beams in the cathode-ray tube of oscilloscope 72. Each verticaldeflection signal has a generally staircase waveform in which thehorizontal portion of each step corresponds respectively to the durationof the scanning period of each drum mirror 22 and the vertical portionof each step corresponds respectively to the spacing between successivebars, or horizontal strips, of object 24 as set by the angle of tilt ofeach drum mirror 22. These deflection signals are synchronized to therotation of the drum 20 by means of a single-frame reflector 78 on drum20 which reflects a pulse of light from lamp 64 to frame photocell 80which then transmits a corresponding triggering pulse to deflectionwaveform generator 76 to trigger the circuitry, not shown, forgenerating each staircase waveform. A well-known fixed bias is appliedin conjunction with the staircase deflection signal to verticaldeflection electrodes of one electron beam of the oscilloscope so thatthe beam deflection is offset vertically by one-half step of thestaircase waveform relative to the deflection of the other beam tocorrespond with the vertical displacement between the two radiationdetectors 33A and 338. Thus, as each individual drum mirror 22 scans ahorizontal strip of the image of object 24, the horizontal strip issubdivided into a set of two narrow, nonoverlapping line scans, asprovided by the two radiation detectors 33A and 333, to give a totalnumber of line scans equal to the product of the number of drum mirrors22 multiplied by the number of radiation detectors 33. For example, drummirrors and two detectors provide a total of horizontal lines in theraster scan displayed on the oscilloscope.

Referring specifically to FIG. 2, there is shown a detailed sectionalview of the optical system taken along the axis of the scanning drum 20and showing in particular the angles of tilt of two drum mirrors 22, theangles being designated a, and a The angles a, and a, which are formedby the intersections respectively of drum mirrors 22A and 228 with theinner surface of the drum, or alternatively by the intersection of anextension of the drum minors with the drum axis, lie in a plane whichcontains the drum axis and which perpendicularly bisects a drum mirrorsuch as the drum mirror 22A or 228.

Referring now to FIG. 3, there is shown an alternative embodiment of theinvention which is illustrated by means of a partial sectional viewtaken along the axis of the scanning drum of this embodiment in whichthe tilted drum mirrors 22 of FIG. 1 are replaced in FIG. 3 withtriangular prisms 82 mounted on drum 20. One surface of each drum prism82 is coated with a metal, such as silver, to fonn a reflecting surface84. Each drum prism 82 is affixed to the inner surface of the drum 20 sothat the reflecting surfaces 84 are flush with the inner surface of drum20. A second surface 86 of each drum prism 82 is inclined at an angle ofinclination with respect to the reflecting surface 84 to deflect or bendthe incident radiation from the inclined mirror 30. The inclinationangle of any one drum prism 82 differs from the corresponding angles ofthe other drum prisms 82 so that each drum prism 82 scans a differentline or strip of object 24. It is shown in FIG. 3 that an incident rayof light from inclined mirror 30 is refracted at the inclined surface86, reflected from surface 84 and again refracted at inclined surface 86as it exits from the prism 82 and is directed to galvanometer mirror 32.The angle between the exit and incident beams determines which line orstrip of object 24 is to be scanned.

Referring now to FIG. 4, there is shown another embodiment of theinvention which is formed by modifying the embodiment of FIG. 1 and isillustrated by means of a partial sectional view taken along the axis ofthe scanning drum of this embodiment. The converging lens 28 of FIG. 1is replaced with a conic section mirror 88, operating as a primaryfocusing means, as shown in FIG. 4, such that an object 91, smaller thanmirror 88, is located between the mirror 88 and the scanning drum 20 ata position near the focal point of the mirror 88 which focuses the raysof radiation in substantially the same fashion as lens 28. Thegalvanometer mirror 32 of FIG. I and the relay system comprising relaymirror 36, relay lens 44 and detector 33 of FIG. 1 are deleted andradiation receiving means in the form of a single radiation detector 89is affixed to the galvanometer torsion support 92, to receive radiationreflected from a tilted drum mirror such as mirror 22A. The outputsignal from radiation detector 89 is applied to a wellknown, single-beamoscilloscope, not shown, to modulate the electron beam of theoscilloscope in the same manner as that utilized for either one of thetwo beams in the embodiment of FIG. 1 for a video picture of object 91.The embodiment of FIG. 4 is advantageous because of the greatersimplicity afforded by the use of fewer components than is utilized inthe embodiment of FIG. 1. However, the embodiment of FIG. 1 has theadvantage of greater scanning speed because of the utilization of aplurality of radiation detectors, and also because the galvanometermirror 32 typically has a lower inertia than radiation detector 89thereby facilitating a rapid oscillatory rotation of galvanometer mirror32.

Referring now to FIG. 5, there is shown an isometric view of analternative embodiment of the invention in which a multiplicity ofradiation detectors 33, four of which are shown in FIG. 5, arevertically displaced from each other with reference to the horizontalline scans and are utilized instead of the two radiation detectors 33shown in FIG. 1. As is seen by a comparison of the embodiments of FIGS.5 and 1, both embodiments utilize the same scanning drum 20, with tiltedmirrors 22, the same reflectors 60 and 78, and photocells 66 and 80,respectively, for synchronization, and the same lenses and mirrors whichproject portions of the image of object 24 to each respectively of thefour radiation detectors 33. The displaying of the signals from the fourradiation detectors 33 of FIG. 5 differs from that shown in FIG. 4 inwhich only one detector is used since the signals from the fourdetectors 33 of FIG. 5 are first combined in a manner that provides forthe display of these signals by means of a single-beam oscilloscope Themanner of combining the signals from the four detectors 33 for displayon the single-beam oscilloscope 94 is best described by a discussion ofthese four signals. It is seen by a comparison of the embodiment of FIG.with those of FIGS. 4 and 1 that in FIG. 4 the single-radiation detector89 is continuously responsive to the image-forming rays of radiationduring the complete period of scanning by each drum mirror such as thedrum mirror 22A, while in FIG. 1 each of the two detectors 33 iscontinuously responsive to the radiation from only one-half of theimage-forming rays of radiation from the galvanometer mirror 32corresponding to two separate elements of object 24. In FIG. 5 each ofthe four detectors 33 is continuously responsive during the completeperiod of scanning by each drum mirror, such as the drum mirror 22A tothe imageforming rays of radiation coming from four contiguoussubelements which, as shown, pass through relay lens 44. It is thereforeevident that by using a large number of detectors, for example 20, eachportion or strip of the image scanned by an individual drum mirror iseffectively subdivided into a large number, 20 in this example, of veryfine, nonoverlapping, parallel strips or line scans. A raster scandisplay utilizing these fine line scans provides a high resolution videopicture of object 24; for example, a scanning drum having mirrorsprovides 10 coarse strips of the image, each of which is subdivided intofine line scans to give a total number of 200 line scans per rasterframe.

It is desirable to modify the four detector signals of FIG. 5 in afashion that permits their display in essentially a simultaneous manneron the oscilloscope 94 which has only one electron beam in itscathode-ray tube, not shown, and can therefore display only one of thefine line scans at a time. Accordingly, the electrical signals generatedby each of the detectors 33 in response to the intensity of detectedradiation are fed by electrical conductors 95 to a well-known samplingunit 96 which sequentially samples and combines, in a well-known manner,the electrical signals of each of the detectors 33 to generate asingle-channel video signal which is transmitted on electrical conductor98 to the beam modulation electrode of the cathode-ray tube ofoscilloscope 94. In essence, the sampling unit 96 is a well-knownelectronic gating or stepping switch which operates by switching rapidlyfrom the signal of one detector'to the signal of another detector andthereby sequentially provides an electrical conducting path from each ofthe detectors 33 to the oscilloscope 94.

The sequential switching is performed in a repetitive pattern in whichthe portion of the image viewed by the first of the detectors 33 issampled again at the conclusion of the sampling of the signal of thefourth of the detectors 33. The repetition period of the samplingsequence has preferably a duration which is related to the movement ofthe image of object 24 projected upon detectors 33 by relay lens 44. Themovement of the image across each of the detectors 33 is provided by themotion of the mirrors 22 on the rotating drum 20. The duration of thesampling repetition period is chosen preferably such that during thisperiod the image has moved a distance of less than one detector width orresolution element, since a longer period would permit the image to movemore than a resolution element leaving a part of the image unsampleduntil subsequent revolutions of the drum 20 when that part of the imagewould be sampled.

A shorter period would permit overlapping coverage of a singleresolution element providing a more precise display of the image as forexample if the sampling sequence is repeated two or three times duringthe scanning of a single resolution element. This process is repeated asthe complete image is scanned horizontally so that, for example, if thesampling sequence of the four detector signals is repeated twice perresolution element, and there is a total of 200 resolution elements in ahorizontal scan by a singledrum mirror 22, then the sampling sequence isrepeated 400 times during the scanning by a single-drum mirror 22 givinga total number of samples for the four detectors of 1,600 samples duringthe scanning period of a single-drum mirror 22.

In order to position the displays of each of the aforementioned signalsamples at their respective locations on the face of the oscilloscope 94in FIG. 5, horizontal and vertical deflection signals are provided toposition the electron beam in the cathode-ray tube of the oscilloscope94. The horizontal deflection signal has the same generally sawtoothwaveform as those described earlier in the descriptions of theembodiments of FIGS. 1 and 4, and is utilized to sweep the electron beamacross the face of oscilloscope 94. The horizontal deflection signal isgenerated by deflection waveform generator 76 in the same manner asdescribed earlier in the embodiment of FIG. I and is synchronized to therotation of the drum 20 by means of the electrical pulses from scan linephotocell 66 whereby a horizontal sweep is provided during the scanningperiod of each drum mirror 22.

The vertical deflection signal positions the electron beam vertically atthe start of the scanning period of each drum mirror 22 so that thevertical position of the electron beam corresponds to the portion of theimage of object 24 that is scanned by a particular drum mirror 22.Furthermore, the vertical deflection signal provides a succession ofrelatively small deviations in the vertical position of the electronbeam which occur respectively at the start of each sampling interval inthe aforementioned sampling sequences of the radiation detectors 33 andhave amplitudes corresponding respectively to each of the spacingsbetween the four fine line scans of the four radiation detectors 33.Accordingly, as the drum mirrors 22 scan successive portions of theimage, the vertical deflection signal is incremented stepwise, as shownin graph 18 of FIG. 6, to display the successive portions of the image.Furthermore, as the sampling unit 96 samples each of the four detectors33 successively in a repetitive sequence, the vertical deflection signalis incremented successively in a repeating sequence of four incrementsor steps, as shown in graph A of FIG. 6, to display corresponding signalsamples from the four detectors 33. The complete vertical deflectionsignal is given by the sum of the fine staircase waveform of graph A inFIG. 6 and the coarse staircase waveform of graph B [N FIG. 6 as isshown by the vertical deflection signal of graph C in FIG. 6. In graph Cthere is also indicated the scanning period of each drum mirror 22 andthe portion of the scanning cycle during which the galvanometer mirrorretrace is effected. The graphs of FIG. 6 show, by way of example, arelationship between the fine and coarse staircase waveforms in whichthe fine staircase is repeating five times per scanning period of eachdrum mirror 22 plus one repetition during each retrace time of thegalvanometer mirror 32. A uniform display of the detector signal samplesis provided throughout the raster scan pattern whether or not the finestaircase waveform and the coarse staircase waveform occur in thesynchronous relationship indicated in FIG. 6.

The fine and coarse staircase waveforms are generated respectively by awell-known sampling staircase generator 100 and the deflection waveformgenerator 76, and are summed together by a well-known summing network102 to produce the vertical deflection signal of graph C in FIG. 6 whichis then applied to the oscilloscope 94 in FIG. 5. Each staircasesequence of the fine staircase waveform is synchronized to the signalsamples of the detectors 33 by means of a succession of 'well-knownsynchronizing pulses from the sampling unit 96 to the sampling staircasegenerator 100. The coarse staircase waveform shown in graph B isgenerated once for each frame of the raster scan and is synchronized tothe rotation of drum 20 by the single frame reflector 78 on drum 20which reflects a pulse of light from lamp 64 to frame photocell whichthen transmits a corresponding electrical triggering pulse to thedeflection waveform generator 76 to synchronize the circuitry, notshown, for generating the coarse staircase waveform.

Referring now to FIGS. 7 and 8, there is shown a further embodiment ofthe invention in which the vertical spacing between the horizontal linescans are provided by a rotating objective lens 104 having prismaticelements 106A and 106B, shown in detail in FIG. 8, for imparting avertical deflection to the rays of light radiated from object 24. Inthis embodiment, drum mirrors 108, which are uniformly arranged alongthe inner surface of drum 20 with their central axes intersecting at acommon point on the drum axis, replace the tilted drum mirrors 22 ofFIGS. 1 and which are no longer required because of the verticaldeflection provided by lens 104.

Lens 104, as shown in a sectional view along the lens axis in FIG. 8, iscomposed of four optical elements, namely the two prismatic elements106A and 1068 which are placed between and in contact respectively withwell-known planoconvex lens 110A and 1108 which focus the radiation fromobject 24 to image at galvanometer mirror 32. Optical elements 106A and110A are held by metallic ring 112A having a bevelled outer edge in theform of a bevelled gear 114A which meshes with drive pinion 116.Similarly, the optical elements 1068 and 1108 are held by metallic ring11213 coaxial with ring 112A and having a bevelled outer edge in theform of a bevelled gear 1148 which also is meshed to pinion 116 so thatthe two rings 112A and 112B are driven by pinion 116 in counterrotation.The prisms 106A and 106B are symmetrically arranged with reference to avertical plane containing the axis 1 of the lens 104 so that as theprisms 106A and 1068 rotate about this axis, their respective base faces118A and 1188 are equidistant from this vertical plane. Thus, when thetwo prism bases 118A and 11813 are at the bottom of lens 104, the raysof light focused by lens elements 110A and 110B are deflected downwards,and when the two bases 118A and 118B are at the top of lens 104 the raysof light are deflected upwards. The prismatic strengths of the prisms106A and 1068 are equal so that at intermediary positions of the bases118A and 1183, that is, when the bases are part way between theaforesaid top and bottom positions, the horizontal deflection componentprovided by prism 106A is cancelled by the oppositely deflectedhorizontal component provided by prism 1068, leaving the desireddeflection of the rays passing through lens 104 at an intermediate anglein the vertical plane only. The prismatic strengths are chosen so thatthe vertical deflection of the rays of light is sufficient to sweep theimage-forming rays of object 24 across the drum mirrors 108 so thatsuccessive horizontal line scans provided sequentially by each of thedrum mirrors 108 are vertically displaced from each other in accordancewith the vertical deflection provided by lens 104.

In operation, therefore, the optical elements of lens 104 focusradiation from object 24 upon the galvanometer mirror 32 by means ofinclined mirror 30 and drum mirrors 108. The optical elements of lens104 are rotated by pinion 116 and lens controller unit 120, to bedescribed below, to continuously sweep the image'forming rays ofradiation past the drum mirrors 108, so that as the scanning drum isrotated by motor 58, each drum mirror 108 reflects a separate horizontalstrip of the image of object 24 to focus upon galvanometer mirror 32. Asin the embodiments of FIGS. 1 and 5, the galvanometer mirror 32 of thisembodiment is cyclically rotated in response to the sawtooth currentfrom generator 68, which is, in turn, synchronized with the rotatingdrum by means of the scan line reflectors 60. The galvanometer mirror 32thereby rotates in synchronism with the rotation of the drum mirrors 108to further reflect the image-forming rays from object 24 to relay mirror36 and relay lens 44 to focus upon radiation detectors 33A and 333. Theoutput signals of detectors 33A and 33B are displayed on dual beamoscilloscope 72 as in the embodiment of FIG. 1. A horizontal deflectionsignal, as is used in the embodiment of FIG. 1, for sweeping eachelectron beam across the face of oscilloscope 72 is generated by awellknown deflection waveform generator 121 which is synchronized to thedrum rotation by means of electrical pulses from scan line photocell 66.The vertical deflection signal for oscilloscope 72 is generated by thelens controller 120 in a manner to be described.

The lens controller unit 120, shown in FIG. 7 and in schematic form inFIG. 8, provides a vertical deflection signal to the oscilloscope 72corresponding with the vertical deflection of the image of object 24provided by lens 104. In addition,

the lens controller imparts a nonlinear rotation rate to lens 104through pinion 116 to compensate for the wellknown nonlinear sinusoidaldeflection rate which is provided by a prism, such as prism 106A and1068, rotating at a constant rate of rotation. Accordingly, the lensrotation rate, as provided by controller 120, is increased at the largerdeflection angles and decreased at the smaller deflection angles in apattern which approximates a secant drive to provide a more linear,vertical deflection rate of rays passing lens 104 than would be the caseif the prisms 106A and 1068 rotated at a constant rate.

A simple form of controller 120, shown within the dashed line in FIG. 8,consists of an eccentric drive, indicated generally by 122, throughwhich a constant rotation rate, provided by electric drive motor 124, isconverted into a nonlinear rotation rate which is then impressed by theeccentric drive 122 upon gear train 126 which, in turn, rotates pinion116. Motor pinion 128 is directly connected to motor 124 and drives abelt 130 which is in contact with the periphery of eccentric 132, sothat the rotation of motor 124 is imparted via pulley 128 and belt 130to eccentric 132. Idler pulley 134 is pressed against belt 130 by aspring, not shown, to take up slack in belt 130 as eccentric 132 rotatesabout eccentric axis 136 which is offset from the center 138 of theeccentric. As is well known, the velocity of the periphery of eccentric132 is constant when the belt slack is taken up by the idler 134, whilethe'angular velocity of gear 140, centered on eccentric axis 136 anddirectly connected to eccentric 132, varies periodically from slow torelatively fast with each revolution of the eccentric. Gear 140 drivesgear 146 which, in turn, is directly connected to pinion 1 16 to impartrotation to lens 104.

The rings 112A and 112B are supported by a rigid structure such ashousing 142, partially shown in FIG. 7, having rollers 144 mounted in awell-known manner to guide and support the rings. Additional well-knownrigid support structures, not shown, are provided for pinion 116 and thecomponents of controller 120.

In order to impart the aforesaid periodic variations in angularvelocity, or rotation rate, to lens 104, the diameters, respectively, ofgear 140 and gear 146 have a ratio equal to one half the ratio of thediameters, respectively, of either gear 114A or 114B to pinion 116 sothat two revolutions of gear 140 produce one revolution each of gears114A and 1148. The eccentric 132 is aligned relative to gears 114A and1148 so that a maximum angular velocity is produced when the prism bases118A and 11813 are at the top of lens 104. Since gear 140 and eccentric132 rotate twice for each revolution of the elements of lens 104, amaximum angular velocity of the elements of lens 104 is also producedwhen the prism bases 118A and 11813 are at the bottom of lens 104.Thereby the desired nonlinearity is imparted to the lens rotation rateby controller 120 such that the rate is increased at the largerdeflection angles and decreased at the smaller deflection angles in apattern which sufficiently approximates a secant drive to compensate forthe nonlinearity of the sinusoidal prism scan to give a more uniformspacing between the horizontal strips of the raster scan displayed onoscilloscope 72.

The vertical deflection signal for oscilloscope 72 is obtained by meansof a well-known synchro 148, shown in FIG. 8, directly connected to gear150 which is driven by gear 146. The ratio of the diameters respectivelyof gears 150 and 146 is the same as the ratio of the diametersrespectively of the gears 114A and 1148 to pinion 116 so that thesynchro rotor, not shown, makes one rotation for each rotation of theelements of lens 104. In addition, the synchro rotor is aligned withgears 114A and 1143 to provide a maximum deflection voltage insynchronism with the maximum deflection of the rays of light by prisms106A and 106B. A well-known synchronous detector 152, energized by thesame source of alternating electric current utilized for synchro 148,converts the synchro output into a positive and negative voltage signalwhich is fed by way of conductor 154 to deflect vertically the beam ofoscilloscope 72. This deflection signal corresponds to the positive andnegative vertical deflection of the optical rays, such as the visible orinfrared rays emitted by object 24, provided by the prismatic elements106A and 1068 of lens 104.

It is understood that the above-described embodiments of the inventionare illustrative only, and that modifications thereof will occur tothose skilled in the art. Accordingly, it is desired that the inventionis not to be limited to the embodiments disclosed herein but is to belimited only as defined by the appended claims We claim:

1, An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, rotatable radiation detection meanspositioned on the axis of said drum to receive image-forming rays ofradiation which are reflected from said reflecting means, at least oneof said reflecting means being adapted to reflect radiation at adifferent angle than the other reflecting means toward said detectionmeans whereby as the drum rotates each of said reflecting means togetherwith said detection means performs a line scan of said image-formingrays, and synchronizing means for synchronizing the rotation of saiddetection means with the rotation of said reflecting means through anangle sufficient to permit sequential detection of radiation during anindividual line scan.

2. An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, radiation detection means including arotatable means positioned to receive image-forming rays of radiationwhich are reflected from said reflecting means, at least one of saidreflecting means being adapted to reflect radiation at a different anglethan the other reflecting means toward said detection means whereby asthe drum rotates each of said reflecting means together with saiddetection means performs a line scan of said image-forming rays,synchronizing means for synchronizing the rotation of said rotatablemeans with the rotation of said reflecting means through an anglesufficient to permit sequential detection of radiation during anindividual line scan, each of said reflecting means being a reflectingsurface, each of said reflecting means being tilted at successivelydifferent angles with respect to the axis of said drum whereby as thedrum rotates each of said reflecting means performs a different linescan.

3. An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, radiation detection means including arotatable means positioned to receive image-forming rays of radiationwhich are reflected from said reflecting means, at least one of saidreflecting means being adapted to reflect radiation at a different anglethan the other reflecting means toward said detection means whereby asthe drum rotates each of said reflecting means together with saiddetection means performs a line scan of said image-forming rays,synchronizing means for synchronizing the rotation of said rotatablemeans with the rotation of said reflecting means through an anglesufficient to permit sequential detection of radiation during anindividual line scan, each of said reflecting means comprising areflecting surface and a prism, a first side of said prism being inspaced relation to said reflecting surface and a second side of saidprism being angularly disposed with reference to said first side, theprisms in each of said reflecting means having first and second sidesdisposed with successively different angularities whereby image-formingrays of radiation are refracted at successively different angles toreflect from the reflecting surface in each of said reflecting means atsuccessively different angles as said drum rotates.

3. An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, radiation detection means positioned toreceive imageforrning rays of radiation which are reflected from saidreflecting means, at least one of said reflecting means being adapted toreflect radiation at a different angle than the other reflecting meanstoward said detection means whereby as the drum rotates each of saidreflecting means together with said detection means performs a line scanof said image-forming rays, said radiation detection means including arotatable mirror, relay focusing system, and a plurality of radiationdetectors, and synchronizing means for synchronizing the rotation ofsaid rotatable mirror with the rotation of said reflecting means throughan angle sufficient to permit sequential detection of radiation duringan individual line scan, the rotatable mirror being locatedapproximately on the axis of the drum and the relay focusing system andbeing positioned relative to the rotatable mirror whereby theimage-forming rays of radiation from said reflecting means are incidentupon the rotatable mirror and reflected by the rotatable mirror throughthe relay focusing system to be detected by the radiation detectors.

5. An optical scanning system providing both horizontal and verticalscan of an object comprising a rotatable drum having a series ofindependent reflecting means located around its circumference, focusingmeans for directing image-forming rays of radiation from said objectsequentially on to each of said reflecting means, radiation detectionmeans including rotatable means positioned to receive image-forming raysof radiation which are reflected from said reflecting means, selectionmeans for progressively directing portions of the image produced by saidfocusing means to said radiation detection means, and synchronizingmeans for synchronizing the rotation of said rotatable means with therotation of said reflecting means through an angle sufficiently large topermit successive detection of radiation of all points along anindividual line scan.

6. The apparatus of claim 5 including means for displaying a raster scanof said image.

7. The apparatus of claim 2 including means for displaying a raster scanof the image produced by said focusing means.

8. The apparatus of claim 5 in which said selection means is combinedwith said focusing means and includes a compound focusing lens havingprismatic portions in which a pair of prisms rotate in oppositedirections about their common optical axis with the same rate ofrotation to refract image-forming rays of radiation from said objectover a continuously varying angle of refraction, each of said prismshaving substantially identical physical forms and being positioned insymmetrical spaced relation whereby the horizontal components of theoptical refraction produced by each prism are made to cancel, and thevertical components of the optical refraction produced by each prismcombine to provide vertical scan.

9. The apparatus of claim 8 including means for displaying a raster scanof the image formed by said focusing means.

10. The apparatus of claim 9 including means for rotating said prismsand means for synchronizing said angle of refraction with the display ofsaid raster scan.

11. A device for scanning approximately linearly across an objectemitting radiation comprising in combination and in optical alignment:primary focusing means which forms an image of said object, firstreflecting means, a rotatable drumshaped housing supporting along itsinner surface a plurality of second reflecting means which are in spacedrelationship, each of the second reflecting means having an orientationrelative to the drum-shaped housing whereby each of the secondreflecting means scans a separate portion of said object as thedrum-shaped housing rotates, radiation receiving means, the primaryfocusing means and the first reflecting means and the radiationreceiving means being so positioned and oriented relative to thedrum-shaped housing whereby the radiation transmitted through theprimary focusing means is reflected by the first reflecting means toreflect sequentially upon each of the second reflecting means and toimage upon the radiation receiving means as the drum-shaped housingrotates, the radiation receiving means being rotatably supported aboutan axis of rotation which is oriented relative to the axis of thedrum-shaped housing whereby the radiation reflected from each of thesecond reflecting means is sequentially incident approximately normallyupon the receiving aperture of the radiation receiving means, and meansto rotate the radiation receiving means in synchronism with the rotationof the drum-shaped housing.

12. A device for scanning approximately linearly across an objectemitting radiation comprising in combination and in optical alignment:primary focusing means which forms an image of said object, firstreflecting means, a rotatable drumshaped housing supporting along itsinner surface a plurality of second reflecting means which are in spacedrelationship, each of the second reflecting means having an orientationrelative to the drum-shaped housing whereby each of the secondreflecting means scans a separate portion of said object as thedrum-shaped housing rotates, third reflecting means, the primaryfocusing means and the first reflecting means and the third reflectingmeans being so positioned and oriented relative to the drum-shapedhousing whereby the radiation transmitted through the primary focusingmeans is reflected by the first reflecting means to reflect sequentiallyupon each of the second reflecting means and image upon the thirdreflecting means as the drum-shaped housing rotates, radiation receivingmeans, the third reflecting means being rotatable about an ar-zis ofrotation which is oriented relative to the axis of the drum-shapedhousing whereby the radiations reflected from each of the secondreflecting means and incident upon the third reflecting means can bereflected by the third reflecting means to the radiation receivingmeans, and means to rotate the third reflecting means in synchronismwith the rotation of the drum-shaped housing.

13. The apparatus as defined in claim 12 including a relay lens andmirror system to transmit the radiation from the third reflecting meansto the radiation receiving means.

14. The apparatus as defined in claim 12 in which the first and thirdreflecting means are adapted whereby the third reflecting means can belocated approximately at the center of the first reflecting means.

15. The apparatus as defined in claim 13 in which the third reflectingmeans is positioned on the optical axis of the primary focusing means toprovide a more linear scan pattern.

16. The apparatus of claim 15 including means for displaying a rasterscan of the image formed by the primary focusing means.

17. An optical scanning system providing vertically displaced horizontalline scans of an object comprising a series of reflecting meanspositioned about an axis with their reflecting surfaces facing saidaxis, focusing means for directing imageforming rays of radiationemitted by said object to form an image of said object upon an imagesurface spaced apart from said focusing means, a movable supportstructure for sequentially carrying each of said reflecting meansbetween said focusing means and said image surface to reflect portionsof said image-forming rays to continuously provide an image at a commonpoint on said axis, detection means positioned on said axis to detectthe radiation emitted by said object, each of said reflecting meanshaving an orientation relative to said movable support structure wherebyeach of said reflecting means scans a different portion of said object,said reflecting means being angled relative to each other such that eachof said reflecting means together with said detection means provides adifferent one of said horizontal line scans.

18. An optical scanning system providing vertically displaced horizontalline scans of an object comprising a series of reflecting means,focusing means for directing image-forming rays of radiation emitted bysaid object to form an image of said object upon an image surface spacedapart from said focusing means, a movable support structure forsequentially carrying each of said reflecting means between saidfocusing means and said image surface to reflect portions of said imageforming rays to continuously provide an image at a common point, anoscillating reflector moving in synchronism with the motion of each ofsaid reflecting means and positioned at said common point to furtherreflect the radiation emitted by said object, detection means includingat least one radiation detector located at a fixed point away from saidcommon point for receiving rays of radiation from said oscillatingreflector, said reflecting means being angled relative to each othersuch that each of said reflecting means together with said oscillatingreflector and said detection means provides a different one of saidhorizontal line scans.

1. An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, rotatable radiation detection meanspositioned on the axis of said drum to receive image-forming rays ofradiation which are reflected from said reflecting means, at least oneof said reflecting means being adapted to reflect radiation at adifferent angle than the other reflecting means toward said detectionmeans whereby as the drum rotates each of said reflecting means togetherwith said detection means performs a line scan of said image-formingrays, and synchronizing means for synchronizing the rotation of saiddetection means with the rotation of said reflecting means through anangle sufficient to permit sequential detection of radiation during anindividual line scan.
 2. An optical scanning system comprising arotatable drum having a series of independent reflecting means locatedaround its circumference, focusing means having an optical axis coaxialwith said drum for directing image-forming rays of radiation onto saidreflecting means from a source of radiation, radiation detection meansincluding a rotatable means positioned to receive image-forming rays ofradiation which are reflected from said reflecting means, at least oneof said reflecting means being adapted to reflect radiation at adifferent angle than the other reflecting means toward said detectionmeans whereby as the drum rotates each of said reflecting means togetherwith said detection means performs a line scan of said image-formingrays, synchronizing means for synchronizing the rotation of saidrotatable means with the rotation of said reflecting means through anangle sufficient to permit sequential detection of radiation during anindividual line scan, each of said reflecting means being a reflectingsurface, each of said reflecting means being tilted at successivelydifferent angles with respect to the axis of said drum whereby as thedrum rotates each of said reflecting means performs a different linescan.
 3. An optical scanning system comprising a rotatable drum having aseries of independent reflecting means located around its circumference,focusing means having an optical axis coaxial with said drum fordirecting image-forming rays of radiation onto said reflecting meansfrom a source of radiation, radiation detection means including arotatable means positioned to receive image-forming rays of radiationwhich are reflected from said reflecting means, at least one of saidreflecting means being adapted to reflect radiation at a different anglethan the other reflecting means toward said detection means whereby asthe drum rotates each of said reflecting means together with saiddetection means performs a line scan Of said image-forming rays,synchronizing means for synchronizing the rotation of said rotatablemeans with the rotation of said reflecting means through an anglesufficient to permit sequential detection of radiation during anindividual line scan, each of said reflecting means comprising areflecting surface and a prism, a first side of said prism being inspaced relation to said reflecting surface and a second side of saidprism being angularly disposed with reference to said first side, theprisms in each of said reflecting means having first and second sidesdisposed with successively different angularities whereby image-formingrays of radiation are refracted at successively different angles toreflect from the reflecting surface in each of said reflecting means atsuccessively different angles as said drum rotates.
 4. An opticalscanning system comprising a rotatable drum having a series ofindependent reflecting means located around its circumference, focusingmeans having an optical axis coaxial with said drum for directingimage-forming rays of radiation onto said reflecting means from a sourceof radiation, radiation detection means positioned to receiveimage-forming rays of radiation which are reflected from said reflectingmeans, at least one of said reflecting means being adapted to reflectradiation at a different angle than the other reflecting means towardsaid detection means whereby as the drum rotates each of said reflectingmeans together with said detection means performs a line scan of saidimage-forming rays, said radiation detection means including a rotatablemirror, relay focusing system, and a plurality of radiation detectors,and synchronizing means for synchronizing the rotation of said rotatablemirror with the rotation of said reflecting means through an anglesufficient to permit sequential detection of radiation during anindividual line scan, the rotatable mirror being located approximatelyon the axis of the drum and the relay focusing system and beingpositioned relative to the rotatable mirror whereby the image-formingrays of radiation from said reflecting means are incident upon therotatable mirror and reflected by the rotatable mirror through the relayfocusing system to be detected by the radiation detectors.
 5. An opticalscanning system providing both horizontal and vertical scan of an objectcomprising a rotatable drum having a series of independent reflectingmeans located around its circumference, focusing means for directingimage-forming rays of radiation from said object sequentially on to eachof said reflecting means, radiation detection means including rotatablemeans positioned to receive image-forming rays of radiation which arereflected from said reflecting means, selection means for progressivelydirecting portions of the image produced by said focusing means to saidradiation detection means, and synchronizing means for synchronizing therotation of said rotatable means with the rotation of said reflectingmeans through an angle sufficiently large to permit successive detectionof radiation of all points along an individual line scan.
 6. Theapparatus of claim 5 including means for displaying a raster scan ofsaid image.
 7. The apparatus of claim 2 including means for displaying araster scan of the image produced by said focusing means.
 8. Theapparatus of claim 5 in which said selection means is combined with saidfocusing means and includes a compound focusing lens having prismaticportions in which a pair of prisms rotate in opposite directions abouttheir common optical axis with the same rate of rotation to refractimage-forming rays of radiation from said object over a continuouslyvarying angle of refraction, each of said prisms having substantiallyidentical physical forms and being positioned in symmetrical spacedrelation whereby the horizontal components of the optical refractionproduced by each prism are made to cancel, and the vertical componentsof the optical refraction produced by eAch prism combine to providevertical scan.
 9. The apparatus of claim 8 including means fordisplaying a raster scan of the image formed by said focusing means. 10.The apparatus of claim 9 including means for rotating said prisms andmeans for synchronizing said angle of refraction with the display ofsaid raster scan.
 11. A device for scanning approximately linearlyacross an object emitting radiation comprising in combination and inoptical alignment: primary focusing means which forms an image of saidobject, first reflecting means, a rotatable drum-shaped housingsupporting along its inner surface a plurality of second reflectingmeans which are in spaced relationship, each of the second reflectingmeans having an orientation relative to the drum-shaped housing wherebyeach of the second reflecting means scans a separate portion of saidobject as the drum-shaped housing rotates, radiation receiving means,the primary focusing means and the first reflecting means and theradiation receiving means being so positioned and oriented relative tothe drum-shaped housing whereby the radiation transmitted through theprimary focusing means is reflected by the first reflecting means toreflect sequentially upon each of the second reflecting means and toimage upon the radiation receiving means as the drum-shaped housingrotates, the radiation receiving means being rotatably supported aboutan axis of rotation which is oriented relative to the axis of thedrum-shaped housing whereby the radiation reflected from each of thesecond reflecting means is sequentially incident approximately normallyupon the receiving aperture of the radiation receiving means, and meansto rotate the radiation receiving means in synchronism with the rotationof the drum-shaped housing.
 12. A device for scanning approximatelylinearly across an object emitting radiation comprising in combinationand in optical alignment: primary focusing means which forms an image ofsaid object, first reflecting means, a rotatable drum-shaped housingsupporting along its inner surface a plurality of second reflectingmeans which are in spaced relationship, each of the second reflectingmeans having an orientation relative to the drum-shaped housing wherebyeach of the second reflecting means scans a separate portion of saidobject as the drum-shaped housing rotates, third reflecting means, theprimary focusing means and the first reflecting means and the thirdreflecting means being so positioned and oriented relative to thedrum-shaped housing whereby the radiation transmitted through theprimary focusing means is reflected by the first reflecting means toreflect sequentially upon each of the second reflecting means and imageupon the third reflecting means as the drum-shaped housing rotates,radiation receiving means, the third reflecting means being rotatableabout an axis of rotation which is oriented relative to the axis of thedrum-shaped housing whereby the radiations reflected from each of thesecond reflecting means and incident upon the third reflecting means canbe reflected by the third reflecting means to the radiation receivingmeans, and means to rotate the third reflecting means in synchronismwith the rotation of the drum-shaped housing.
 13. The apparatus asdefined in claim 12 including a relay lens and mirror system to transmitthe radiation from the third reflecting means to the radiation receivingmeans.
 14. The apparatus as defined in claim 12 in which the first andthird reflecting means are adapted whereby the third reflecting meanscan be located approximately at the center of the first reflectingmeans.
 15. The apparatus as defined in claim 13 in which the thirdreflecting means is positioned on the optical axis of the primaryfocusing means to provide a more linear scan pattern.
 16. The apparatusof claim 15 including means for displaying a raster scan of the imageformed by the primary focusing means.
 17. An optical scanning systemproviding verticalLy displaced horizontal line scans of an objectcomprising a series of reflecting means positioned about an axis withtheir reflecting surfaces facing said axis, focusing means for directingimage-forming rays of radiation emitted by said object to form an imageof said object upon an image surface spaced apart from said focusingmeans, a movable support structure for sequentially carrying each ofsaid reflecting means between said focusing means and said image surfaceto reflect portions of said image-forming rays to continuously providean image at a common point on said axis, detection means positioned onsaid axis to detect the radiation emitted by said object, each of saidreflecting means having an orientation relative to said movable supportstructure whereby each of said reflecting means scans a differentportion of said object, said reflecting means being angled relative toeach other such that each of said reflecting means together with saiddetection means provides a different one of said horizontal line scans.18. An optical scanning system providing vertically displaced horizontalline scans of an object comprising a series of reflecting means,focusing means for directing image-forming rays of radiation emitted bysaid object to form an image of said object upon an image surface spacedapart from said focusing means, a movable support structure forsequentially carrying each of said reflecting means between saidfocusing means and said image surface to reflect portions of said imageforming rays to continuously provide an image at a common point, anoscillating reflector moving in synchronism with the motion of each ofsaid reflecting means and positioned at said common point to furtherreflect the radiation emitted by said object, detection means includingat least one radiation detector located at a fixed point away from saidcommon point for receiving rays of radiation from said oscillatingreflector, said reflecting means being angled relative to each othersuch that each of said reflecting means together with said oscillatingreflector and said detection means provides a different one of saidhorizontal line scans.